The pulsator mechanism of the double-action milking machine causes the rhythmical expansion and collapse of the rubber teat-cup liner during milking by alternately applying a partial vacuum (usually 13–15 in. Hg) and admitting atmospheric air to the space between the rubber liner and the teat-cup shell. The inside of the liner is subjected to continuous partial vacuum.

It is now some 6 years since the appearance in this series of a Review of Bacteriology and Mycology applied to Dairying (1) with sections on milk control, detergents and disinfectants, and pasteurization. Nearly 12 years have elapsed since a complete Review (2) including all the sections listed above was published in the Journal of Dairy Research; some attempt has been made to deal with the more important work going back to these Reviews.